1. Field of Invention
The present invention relates to a process for forming a conductive film, and more particularly a process for forming a metal film used for the electrodes and/or wiring of a semiconductor device, especially a semiconductor integrated circuit.
2. Description of Prior Art
Aluminum and doped polycrystalline silicon have conventionally been used for the conductive film mentioned above. One of the new materials, which has recently been found to be suitable for the conductive metal film mentioned above, is a silicide of a transition metal, particularly a refractory metal, such as tungsten and moleybdenum. The transition metal silicide has a lower resistance than the polycrystalline silicon, which is frequently used as the electrode material of an insulated gate field effect transistor (IG FET). In addition, the transition metal silicide is stable at an elevated temperature and exhibits a fine grain size. Accordingly, the transition metal silicide can be shaped into a fine electrode and circuit pattern, and thus, plays more and more of an important role in the production of a highly integrated, high speed semiconductor device. Another of the new materials is an aluminum silicon alloy which contains from 2 to a few percent of silicon. The addition of silicon to the aluminum can prevent undesirable reactions, which occur between the electrode metal and the semiconductor substrate, for example, during sintering of the electrode metal. Accordingly, the aluminum silicon alloy is attractive for the production of a highly integrated, high speed semiconductor device, such as an integrated circuit.
It is known that a transition metal silicide film or an aluminum silicon alloy film can be produced by one of the processes of: (a) vacuum evaporation of a metal or alloy composition which is locally heated by an electron gun; (b) simultaneous vacuum evaporation of the two components of the alloy or silicide from different evaporation sources with the aid of electron guns; (c) vacuum evaporation of the alloy by a flashing method, wherein the metal or alloy powders are dispersed onto a heater, flashed and evaporated by the heater, and; (d) sputtering of a target consisting of the alloy.
Processes (a) and (c) mentioned above are commonly disadvantageous due to the fact that, in repeated deposition of the film of the alloy on the substrate, for example a semiconductor substrate, the reproducibility of the alloy composition is too low.
Processes (a) and (b) mentioned above are commonly disadvantageous, due to a secondary electron emission from the vaporization source the semiconductor substrate is damaged. This is one of the causes of: dispersion of the resistance value of the film made of alloy; deterioration of electrical properties of the semiconductor element which is formed on the surface of the semiconductor substrate, and; a decrease in reliability of the semiconductor device.
It is recognized by experts in the semiconductor device field that, according to the process (d), the transition metal silicide or the aluminum silicon alloy film can be produced repeatedly with excellent reproducibility of the film composition because the same composition as that of a target made of the silicide or alloy is sputtered from the target and deposits on the semiconductor substrate. However, the silicon content of the film cannot be adjusted optionally unless the target composition is changed.